The electrohydrodynamic (EHD) phenomena involve the interaction of electric fields and flow fields in a dielectric fluid medium. This interaction between electric fields and flow fields can induce the flow motion by electric body force. In general, there are three kinds of EHD pumps operating based on the Coulomb force; induction pumping, ion-drag pumping, and pure conduction pumping.
EHD induction pumping relies on the generation of induced charges. This charge induction in the presence of an electric field takes place due to a non-uniformity in the electrical conductivity of the fluid. Non-uniformity in the electrical conductivity can be caused by the non-uniform temperature distribution and/or an inhomogeneity of the fluid, such as in a two phase fluid. Therefore, induction pumping can not be utilized in an isothermal liquid.
Ion-drag pumping may be used for generating a space charge in an isothermal liquid. Ion-drag pumping generally includes ion injection at a metal/liquid interface for generating the space charge in the isothermal liquid. However, ion-drag pumping is not desirable because it can deteriorate the electrical properties of the working fluid.